1. Field of the Invention
The present invention relates to optical component design and more particularly to a waveguide and a method for producing it by tailoring the optical field intensity (OFI) of a guided wave using selected block copolymers, or block copolymers in combination with homopolymers, that are processed above the highest glass transition temperature T.sub.g of any component to form unique morphologies.
2. Prior Art
Diblock, AB, triblock, ABC, or multiblock copolymers are known to form unique morphologies when phase separation occurs. The size, shape, and spacing of the microdomains that result can be controlled through selection of the relative molecular weights of the various block copolymer components. The phase separation of the various components is driven by the thermodynamic incompatibility of their chemical components. For example, poly(styrene), PS, and poly(methylmethacrylate), PMMA, are homopolymers that are normally incompatible and hence usually will not mix to form a stable phase. If they are chemically connected to each other by covalent bonding through a chain end, then they are considered to be an AB block copolymer. When rapidly cast from solution they will form a thermodynamically unstable single phase which, when heated or otherwise brought above the glass transition temperature, T.sub.g, will separate into microdomains that, for example, can be rodlike, spherical, bicontinuous cubic, lameliar, or otherwise, in shape. In certain instances the phase separation in AB block copolymers will yield stacked lamella consisting of alternating A and B slabs or layers with different refractive indices as shown in FIG. 1 wherein poly(styrene) and poly(methylmethacrylate) form the slabs. In addition, if such copolymers are roll cast from solution, then well ordered, globally oriented microdomains can be formed (see R. Albalak and E.L. Thomas, J. POLYMER SCI (Phys). 31, 37 (1993)). Other known means of globally orienting lamellar films are surface-induced ordering, mechanical, such as shear, alignment, and electric field or magnetic field alignment.
While these thin film features and characteristics are known in the art, heretofore, there has been little done toward applying such features in special waveguides and related devices (optical elements, etc.).
In this regard, an important parameter which has been shown to effect the waveguiding characteristics of a slab is the thickness (see J. F. Rabolt et al, APPLIED SPECTROMETRY, 34, 517 (1980)). In the case of diblock or triblock copolymers it would therefore appear that the relative thickness of the respective A and B, or A, B, and C, slabs should be variable by selecting the relative molecular weights of the various blocks, or by using a diluent (cOmpatible solvent, homopolymer, etc.) to selectively swell individual A, B, or C slabs. By adjusting both the individual slab thickness and its refractive index, through choosing suitable component parameters, the guided wave characteristics of a waveguide should then be tailorable for specific applications.